[ELF][Writer] Don't infinite loop.
[ELF][Writer] Don't infinite loop.

This will be tested by a following committ that runs the linker
with no inputs.

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@171576 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld